Loans - Schedule of Loan Portfolio (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 29,699,208	$ 25,035,469
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,825,997	4,331,032
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	17,643,759	13,895,407
Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	15,996,741	12,407,275
Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,647,018	1,488,132
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,377,111	4,111,400
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,852,341	2,697,630
Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	487,272	517,089
Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,451,623	1,319,571
Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	913,446	860,970
Non-PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	23,069,609	20,845,383
Non-PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	4,143,983	3,590,375
Non-PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	12,398,610	11,034,657
Non-PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	10,902,893	9,912,309
Non-PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,495,717	1,122,348
Non-PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	3,796,942	3,682,984
Non-PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	2,730,074	2,537,367
Non-PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	376,020	371,340
Non-PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	1,451,352	1,319,206
Non-PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	902,702	846,821
PCI Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	6,629,599	4,190,086
PCI Loans | Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	682,014	740,657
PCI Loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,245,149	2,860,750
PCI Loans | Commercial real estate | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	5,093,848	2,494,966
PCI Loans | Commercial real estate | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	151,301	365,784
PCI Loans | Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	580,169	428,416
PCI Loans | Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	122,267	160,263
PCI Loans | Consumer | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	111,252	145,749
PCI Loans | Consumer | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	271	365
PCI Loans | Consumer | Other consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans	$ 10,744	$ 14,149